This invention relates to a capacitive sensor for determining the position of a moving element, for example, the rotor of an electromechanical actuator.
In typical capacitive sensors, for example, the one shown in Brosens, U.S. Pat. No. 4,135,119, four identical stationary curved plate electrodes are arranged around the lower end of the rotor with their inner surfaces facing the rotor. Each plate is electrically connected to the plate on the opposite side of the rotor. Thus there are two pairs of plates. The rotor has a pair of pole faces. Each pole face cooperates with two of the plates, one from each pair, such that the difference in the capacitances between the pole face and each of the two plates is a function of the rotor's angular position. In typical applications the four plates are soldered at their bases to a printed circuit board and are supported by an epoxy potting material.
It has also been proposed to form the electrode plates on two identical rings that are stacked axially (but with one rotated relative to the other). The rotor pole faces then would cooperate with the plate surfaces on the two rings to provide the desired capacitance differential.